The present invention relates to a control method for plural numbers of compressors, being connected in parallel with each other, and a compressor system according thereto.
An example of such the compressor system, in which plural numbers of compressors are connected in parallel, is described in Japanese Patent Laying-Open No. 2000-12583, for example. In this publication, the requested flow rate is divided into plural numbers of flow adjustment regions, so that the sum of the maximum values of supply flows of the compressors operating comes to be equal to or greater than that requested flow, and also the number of the compressors operating comes to the minimum. And, also with this, for each of the flow adjusting regions is preset or provided a flow control pattern, which indicates a combination of those operating compressors, as well as, a control condition of each of the operating compressors, thereby the each compressor is controlled in accordance with that preset pattern. In the case including the compressor(s) therein, on which can be obtained only ON/OFF control, the compressor(s), on which can be obtained a constant gas pressure, as well as, the ON/OFF control, is determined to be a machine(s) for use in flow rate adjusting. In a region(s) neighboring to the region in the flow rte, which is preset to this compressor, the compressor(s), on which can be obtained only ON/OFF control, is/are used as the machine(s) for use in flow rate adjusting, with priority. With this, it is possible to lessen the waste of pressurized gas during unload operation, as well as, to enable to protect the plural numbers of compressors from rushing into a surge waiting condition simultaneously, as far as possible.
In the control method for the plural numbers of compressors described in the publication mentioned above, the characteristic on flow rate is determined for each of the plural numbers of compressors, and each of those compressors is controlled with using the preset flow rate control pattern on the basis of the characteristic thereof. However, due to interior conditions of the compressor, such as, unclearness or dust inside the compressor machine, etc., and/or external conditions, such as, fluctuations in temperature and pressure on gas flowing into the compressor for each season, etc., there occurs occasion that the actual operation point of each compressor differs from that expected. In such case, trying to control the compressor compulsively by using the predetermined control patter causes the situation that the operation point reaches to the surge limit earlier that expected, and/or that the compressor(s) is brought into an unloaded operation very much before that surge limit. As a result of this, there are risks of bringing about drawbacks that each compressor consume useless motive power, and/or that the compressor operates unstably due to sudden rushing of the surge.
An object, according to the present invention, by taking the drawbacks of such the conventional arts as mentioned above into the consideration thereof, is to provide a compressor system having plural numbers of compressors, wherein a partial load control is made easy by means of a simple control system. Other object, according to the present invention, is to provide a compressor system having plural numbers of compressors, wherein power consumption can be reduced. Further other object, according to the present invention, is to operate the plural numbers of compressors effectively under the situation where the operating conditions fluctuate. And the present invention is made for accomplishing at least one of those objects mentioned above.
According to the present invention, for accomplishing the above object mentioned above, there is provided a control method for plural numbers of compressors, comprising the following steps of: decreasing down flow rates of all the compressors which are driven under load operating condition, when a load of plural numbers of the compressors goes down; bringing the compressor, which rushes into surge at the earliest, into an un-load operating condition; and increasing up the load of the compressors other than that brought into the un-load operating condition, thereby enabling an operation depending upon the load.
Also, according to the present invention, in the control method for plural numbers of compressors defined in the above, preferably, wherein said plural numbers of the compressors are turbo compressors, and said method further comprises the following steps of: obtaining surge limit of at least one of the compressors in advance; and memorizing the surge limit into memory means, wherein the flow rate is decreased down quickly until a point where the flow rate is larger than the surge limit memorized in said memory means by a predetermined amount, when decreasing down the flow rate generated by the compressor as the load comes down, and thereafter is changed more slowly than a period before, until a time of rushing into surge of generating surge.
Further, according to the present invention, in the control method for plural numbers of compressors defined in the above, wherein the surge limit data memorized in said memory means may be an opening angle of inlet guide vanes, and the surge limit data memorized in said memory means may be renewed by the opening angle of the inlet guide vanes of when rushing into the surge; wherein in a case of the compressor having the surge limit data obtained in advance among the plural numbers of the compressors, the data may be memorized in said memory means, while in a case of the compressor having no surge limit data, the data of the compressor having the surge limit data therein is applied to in place thereof; wherein the compressors are started in an order of rushing into the surges and brought into the un-load operating condition, when all the compressors are stopped and then they are started again; wherein the compressors under the un-load operating conditions are brought into the load operating conditions in an order of rushing into the surge earlier, when turning them back, if the compressors under the un-load operating conditions are plural in number thereof while the load increases up; and wherein the flow rate is reduced down so as to rush into the surge, and it is turned back to that at the time just before rushing into the surge, after once rushing into the surge, while a blow-off valve is opened, when the compressor under load operating condition is one (1) and the load goes down, thereby enabling control depending upon the load.
Also, according to the present invention, for accomplishing the object mentioned above, there is provided a control method for plural numbers of compressors, comprising the following steps of: observing power consumed in each compressor by decreasing flow rates of all the compressors driven under load operating condition down to a surge limit memorized in memory means in advance, when a load of the plural numbers of the compressors goes down; bringing the compressor showing the largest power consumption into an unload operating condition; and increasing up the flow rates of the compressors other than that brought into the unload operating condition, whereby enabling an operation depending upon the load.
Further, according to the present invention, there is provided a compressor system having plural numbers of compressors connected in parallel, comprising: surge detection means provided at discharge side of each of the plural numbers of compressors; and a controller means for controlling each of said plural numbers of compressors, so that a load for each of all the compressors is reduced down when a load of said compressor system goes down and the compressor rushing into surge at first is brought into an unloaded operating condition, while increasing up the loads of the other compressors.
And, also in the compressor system as defined in the above, preferably, wherein each of said plural numbers of compressors is a turbo compressor having an inlet guide vanes at a suction side thereof, and said controller means gives an instruction of rotation angle to the inlet guide vanes depending upon change on the load of the each compressor; further comprising a discharge-pressure detection means of the compressor system, provided in a downstream side from a junction position of said plural numbers of compressors connected in parallel, wherein said controller means gives an instruction of rotation angle to each of the inlet guide vanes, so that the discharge-pressure comes to be a predetermined pressure; and wherein said controller means has memory means for memorizing surge limit therein.